Chapter 2 of this thesis provides more details on the Solar Toilet prototypes and their testing under field conditions in India and China. The general concept, specific design elements, and treatment approach proven to be viable for the treatment of raw domestic wastewater, human urine, and human feces. After several hours of photovoltaic-powered (PV-powered) electrochemical treatment, the turbid, black- water influent can be clarified with the elimination of the suspended particles along with the reduction or total elimination of the chemical oxygen demand (COD), total enteric coliform disinfection via in situ reactive chlorine species generation, and the elimination of measurable protein after 3 to 4 hours of electrochemical treatment.
In Chapter 3 of this thesis, the energy efficiency of the Solar Toilets is improved by the addition of a microbial fuel cell system for urine pre-treatment. The microbial fuel cell system used consists of two stacks of 32 fuel cells connected in parallel. The pre-treatment of human urine by anodic microorganisms occurred with concomitant electrical energy recovery. This usage of microbial fuel cells can lower the energy cost for treating human waste while recovering the necessary electrical energy to divert the urine flow, making this approach an overall energy gain for the entire onsite self- contained human waste treatment system.
Chapter 4 of this thesis provides information on nutrient recovery from the Caltech Solar Toilets. It describes the co-production of crystallized Mg-containing hydroxyapatite during the treatment of wastewater. The purpose of this study was to evaluate the potential for phosphate removal from human wastewater during electrochemical treatment using the same combined anode-cathode system
described in Chapter 2. Phosphate-containing precipitates were identified and phosphate removal efficiencies were measured in authentic and synthetic toilet wastewater. Experiments in synthetic wastewater allowed quantification of the effects of ion composition, buffering capacity, current density, and electrode surface area to volume ratio on phosphate removal kinetics and equilibria.
Chapter 5 of this thesis provides more practical applications of my work in developing the Caltech Solar Toilets. A key finding from the field studies of Chapter 2 was the need for a maintenance plan. I and several of my coworkers are developing a smart maintenance technology for onsite wastewater systems. Another key finding from Chapter 3 was that the use of a MFC system for pre-treating urine could be even more effective and easier to install in a Solar Toilet if all the flush water could enter the MFC. This approach is under investigation. The development of a standard on
“Reinvented Toilets” is also addressed in Chapter 5.
Table 1.1: Description of the Caltech Solar Toilet prototypes of different generations (Gen.) with manufacturing and field partners in the USA, India, China, and South Africa.
Map ref.
Gen. Configuration Testing Manufacturing and
field partners Location Period
PAS 1 PV-powered self-
contained bathroom with wastewater treatment and recycling unit in a
shipping container. Design for 40-60 users/day.
Pasadena, CA,
USA 06/2013 to
06/2017 -
KYM Kottayam,
Kerala, India 04/2014 to
01/2016 Mahtamah Gandhi University of Science and Technology
YXG Yixing,
Jiangsu, China 12/2014 to
05/2015 Yixing Eco-Sanitary Manufacture Co.
AMD 1 Grid-powered wastewater treatment and recycling unit connected to an
“eToilet” public toilet (Eram Scientific, Trivandrum, Kerala, India). Design for 40 users/day.
Ahmedabad,
Gujarat, India 04/2014 to
01/2016 Eram Scientific and Indian Institute of Technology (IIT) Gandhinagar
COI 2 Grid-powered wastewater treatment and recycling unit connected apartment buildings. Designed for 5 families.
Coimbatore, Tamil Nadhu, India.
10/2015 to 08/2017
The Kohler Company (design and
construction) and RTI International (field testing).
YXG 2 PV-powered self-
contained bathroom with wastewater treatment and recycling unit in a
shipping container with advanced
anaerobic/aerobic pre- treatment. Designed from 40-60 users/day to 200 users/day.
Yixing, Jiangsu, China
05/2015 to present
Yixing Eco-Sanitary Manufacture Co.
COI 3 Grid-powered wastewater treatment and recycling unit with advanced anaerobic/aerobic pre- treatment connected apartment buildings.
Designed for 5 families.
Coimbatore, Tamil Nadu, India.
10/2017 to present
The Kohler Company (design and
construction) and RTI International (field testing).
DUR 3 PV-powered self-
contained bathroom with wastewater treatment and recycling unit in a
shipping container with advanced
anaerobic/aerobic pre- treatment. Designed from 40-60 users/day to 200 users/day.
Durban, South Africa
01/2018 to present
Yixing Eco-Sanitary Manufacture Co. (design and construction) and Water Research Council for South Africa (field evaluation).
Figure 1.1: Percentage of a country’s population without access to safe sanitation in 2015 according to the World Health Organization (World Health Organization 2015). Location of the prototype testing sites across the world: AMD, Ahmedabad, Gujarat, India; COI, Coimbatore, Tamil Nadu, India; DUR, Durban, Kuazulu-Natal, South Africa; KYM, Kottayam, Kerala, India;
PAS, Pasadena, California, USA; YXG, Yixing, Jiangsu, China.
Figure 1.2: Trends in global drinking water (a) and sanitation (b) coverage and Millenium Development Goal target coverage (%), 1990-2015. Reproduced from Progress on sanitation and drinking water: 2015 update and MDG assessment with the permission of the World Health Organization and UNICEF (World Health Organization, 2015).
Figure 1.3: “Proportion of population accessing difference types of drinking water, by region and by microbial contamination level, 2012. AFR: Africa; AMR: Americas; EMR: Eastern Mediterranean; EUR: Europe; SEAR: South East Asia; WPR: Western Pacific. Microbially contaminated water has detectable E. coli or thermotolerant coliforms in a 100 mL sample, while samples showing no detectable faecal indicator bacteria (<1 per 100 mL) are compliant with WHO guideline values and most national standards.” Reproduced from Preventing diarrhoea through better water, sanitation and hygiene: exposures and impacts in low-and middle-income countries with the permission of the World Health Organization (World Health Organization, 2014).
Figure 1.4: Proportion of the global population using sanitation facilities meeting specific criteria for safely managed services. Reproduced from Progress on drinking water, sanitation and hygiene: 2017 update and SDG baselines with the permission of the World Health Organization (WHO/UNICEF JMP, 2017b).
17
Figure 1.5: Sanitation value chain (top) and Shit Flow Diagram (SFD) for the city of Dhaka, Bangladesh. Reproduced with the permission of The World Bank Group (Blackett et al., 2014).
www.wsp.org
S ervice Delivery Assessment Scorecard
The second analysis tool used was the Service Delivery Assessment (SDA) scorecard (Figure 3).3 This tool ana- lyzes the enabling environment, the level and management of budgets and other inputs needed to develop adequate fecal sludge management services, and the factors con- tributing to service sustainability.4 The scorecard was ap- plied to each step of the sanitation service chain, resulting in a two-dimensional matrix in which bottlenecks and gaps at any point along the chain are identified and classified according to whether the issues are in the enabling envi- ronment, in service development, or in sustaining services.
3 The SDA was originally developed to provide a national-level overview of the quality of urban and rural sanitation and water supply service delivery.
4 The tool generates a score ranging from zero (worst case) to three (best case) in response to a set of specific questions relating to components of the enabling environment (policy, planning, budget), development of services (expenditure, equity, outputs), and sustainability of services (maintenance, service expansion, user outcomes). It uses a red, amber, and green color- coding to highlight the scores.
Containment Emptying Transport Treatment Reuse/
Disposal
On-site facility
defecationOpen
Safely
emptied Illegally
dumped Leakage
Unsafely emptied
Left to overflow or abandoned WC to
sewer
2%
9%
1% 69% 9% 9% 1%
Receiving waters Drainage
system Residential
environment
1%%
effectivelyNot treated Effectively
treated
Figure 2: Fecal Waste Flows in Dhaka, Bangladesh
Policy
Containment Emptying Transport Treatment Disposal
Planning Budget
Enabling
1 0 0
0.5 0 0
0.5 0 0
0 0 0
0 0 0
Expenditure Equity Output
Developing
0 0 0
0 0 0
0 0 0
0 0 0
0 0 0
Maintenance Service expansion User outcomes
Sustaining
0.5 0 0.5
0.5 0 0.5
0.5 0 0.5
0 0 0
0 0 0 Good Improving Poor
Figure 3: Fecal Sludge Management Scorecard for Dhaka, Bangladesh
8933-WSP Fecal Sludge.pdf 3
8933-WSP Fecal Sludge.pdf 3 4/28/14 12:57 PM4/28/14 12:57 PM
20%
79%
1%
Figure 1.6: Waterborne and foodborne diseases transmission and control. (Water Supply and Sanitation Collaborative Council & World Health Organization, 2005)
Figure 1.7: System flow diagram of the 2014 Caltech Solar Toilet prototypes with capacity and residence time of the relevant components. Relevant components to chapters 2, 3, and 4 of this thesis are highlighted with a different color. Chapter 2 (black): design and preliminary implementation of onsite electrochemical wastewater treatment and recycling toilets for the developing world. Chapter 3 (red): urine microbial fuel cells in a semi-controlled environment for onsite urine pre-treatment and electricity production. Chapter 4 (blue): phosphate recovery from human waste via the formation of hydroxyapatite during electrochemical wastewater treatment.